It is indispensable for an electrical electronic component used widely in vehicles and electrical appliances to be electrically insulated from outsides for satisfying its use purpose. For example, an electrical wire is coated with a resin having an electrical insulation property. Today, applications in which electrical electronic parts with complicated shapes are required to be packed in a small capacity, e.g., mobile phones, are sharply increased and in such a situation, various methods for their electrical insulation are employed. In particular, when an electrical and electronic part such as a circuit board having a complicated shape is sealed with a resin which serves as an electrical insulator, a sealing method in which the resin certainly flows along the shape of the electrical and electronic part without causing short shot is required, and the resin is needed to have such a adhesive durability that an electrical insulating property would be maintained for an extended period of time. For that, it is common to employ a method for decreasing the viscosity of a sealing resin composition at the time of coating. A hot melt resin for sealing whose viscosity is lowered only by heating and melting to make sealing possible can be solidified to give a sealed body merely by cooling after sealing and thus has a high productivity, and in addition, since a thermoplastic resin is commonly used therefor, the resin can be melted and removed by heating after the life as a product is finished, thereby easily making recycling of the component possible.
Having both a high electrical insulation property and water-proofness, a polyester is supposed to be a very useful material for the above-mentioned application; however, in general, a polyester has a high melt viscosity and it is necessary to carry out injection molding at a high pressure of several hundred MPa or more in the case of sealing a component with a complicated shape, and there is a risk of breaking an electrical electronic part. Patent Document 1 discloses an adhesive composition for a structure, containing a specified polytetramethylene glycol copolymerized polyether ester elastomer and an epoxy compound having at least 1.2 or more of glycidyl groups on a number average basis in the molecule. Herein, the polyester resin used herein has good initial adhesive property but tends to have high crystallinity, and thus generates strain energy at the time of transfer from the amorphous state to the crystalline state after bonding, and therefore, the adhesive strength tends to be lowered significantly and the polyester resin is unsuitable for a sealing material for electrical electronic parts.
Patent Documents 2 and 3 propose a hot melt resin composition for sealing having a melt viscosity that enables sealing at a low pressure so as not to damage electrical electronic parts. The resin composition allows molded components with good initial adhesive property to be obtained and allows a polyester-based resin composition to be applied to common electrical electronic parts. However, these materials for sealing electrical and electronic parts have a problem that, despite often being required to have flame retardancy because of apprehensions about tracking or the like, they have high flammability.
Patent Document 4 discloses a resin composition for sealing electrical and electronic parts which contains a crystalline polyester resin, an epoxy resin, and a polyolefin resin are blended. This composition is high in adhesive strength, but has, similarly to the above-mentioned compositions, the drawback of having very high flammability.